Lisa, big boring machine digs passage under SF Valley

By: Kamala Kelkar

A 160-ton tunnel-boring machine named Lisa will begin carving an underground path Monday for a new sewage pipe about 40 feet below Visitacion Valley.

Named after its owner’s wife, Lisa will cut a 12-foot-wide tunnel designed to relieve neighbors of persistent sewage backups during rainy seasons. The passageway will stretch about 4,000 feet from Bayshore Boulevard to Harney Way, near Candlestick Park.

The current pipe, which was built in 1913, is about half the diameter of the new one being laid. Utility workers say it isn’t big enough.

“It’s an old system,” said Manfred Wong, a senior project manager with the San Francisco Public Utilities Commission. “The water floods the streets, gets in garages … sometimes toilets are backed up.”

The agency’s new Sunnydale Auxiliary Sewer Tunnel is a $53 million project expected to be finished by early 2012. It will act as a backup to the existing pipe.

Lisa will dig under homes, businesses, Caltrain tracks, U.S. Highway 101 and other objects. About eight people ride in it, while still more make sure debris is removed and air is pumped to their underground colleagues. The debris moves via conveyer belt to “muck trucks” that send it back to base via underground rail.

“Nobody above will feel a thing,” agency spokesman Tyrone Jue said.

Lisa was built in Canada and had to be driven here because it couldn’t fit through train tunnels, said Gregg Rehak of Super Excavators Inc.

Today, the SFPUC is inviting anyone who wants to ogle the massive machine to come to the site at 11 a.m. Visit SFWater.org to RSVP.

Visitors will wear construction hats, orange vests and glasses as they are escorted down a narrow set of steps to the base of the tunnel where Lisa was lowered, about 40 feet below ground. They will see the innards of the machine, the generators that power it, and the levers, chains, switch systems and devices used for navigation.

They will not, however, see the 22 “rippers” and other blades that slice through rock, concrete and anything else that stands in its way, because the front end is already engaged.

The project has been 10 years in the making. Jue said the outdated sewer line has been a problem longer than that.